you dont actually need the spacers if you want do do it cheap. after blowing up 3 10 bolts i did the swap. i did it to my 02 silverado rather easly. heres a pic and a few pointers from what i learned
first make sure the axle is from a 1500 hd 6 lug and not the 2500ld. the axle in the 2500 ld that is six lug is to narrower and your spring perches are to wide. if you run to inset of a wheel your rims will hit the leafs. so youll eather have to get 1.5-2 inch wheel spacer/adapters or find the right axle out of a 1500
second you dont really need the spacers for the caliper mount assembly. every mount on the axle needs to be cut off anyway. (spring perches are too narrow, shocks were on the wrong side of the tube, at least for my truck and mine had bottom out landing plates i no longer needed.) i just took my cut off wheel and die grinder and cut the welds off the existing plates. cleaned the tubes outside of them, and slid the existing mounts out. its a little more time consuming but to me it seemed a lot more solid than making a spacer. just make sure its perfectly square and that the caliiper and bracket is positioned where you want it before you burn it in.
third loosly mount it in your truck before you burn in the perch mounts. make sure you pinion angle and shock mounts ar right where you want um and burn it all in. i went the cheap way when i did it and bought the conversion joint for the drive shaft to make it work instead of replacing the yoke or driveshaft.
last make sure you replace all the bearings, seals and brakes while you have it apart. its completly disassembled before install so why not right.
also from my learnings and this may not be true everywhere but most of the sf 14 bolts around here from the 99+ vortec maxes, denalis ect had drum brakes in the rear.i think you will still have to move the brake mount on the axle or get a spacer. but the spring perches and shock mounts should be in the correct spot. but as i said i may be wrong.
hope that helps